Against the background of a low-carbon society, the types of electrical storage devices have diversified to include nickel-hydride batteries, lithium ion batteries, electric double layer capacitors, and the like. The application field of electrical storage devices has also expanded from the conventional portable devices to home appliances, backup power supplies, electric vehicles (EV), hybrid electric vehicles (HEV), and smart grids, and applications as large power supplies have demonstrated particularly significant expansion.
Electrical storage devices for use as large power supplies are more expensive and required to withstand longer use than the conventional power supplies for portable device. Therefore, it is also important from the standpoint of maintenance and inspection to predict more accurately the life of electrical storage devices.
However, the life of an electrical storage device is greatly affected by the material, structure and the like of the electrical storage device (referred to hereinbelow as “type of electrical storage device”) and also temperature, charge/discharge final voltage and the like (referred to hereinbelow as “operation conditions of electrical storage device”). Therefore, it is important to predict the life of an electrical storage device by taking into account the type and operation conditions of the electrical storage device.
In the conventional method, the life of an electrical storage device is predicted by periodically discharging the electrical storage device during the use and performing diagnostics by comparing the pulsation amplitude of an output current and a terminal voltage with base data at the time of shipping (see, for example, Patent Literature 1).
In another conventional method, the relationship between the internal resistance of an electrical storage device and the elapsed time is measured at a plurality of points in time, an approximation formula for the relationship is created, and the time at which the internal resistance of the electrical storage device becomes equal to or greater than a predetermined internal resistance value is determined as the life of the electrical storage device (see, for example, Patent Literature 2).
In yet another conventional method, main factors affecting the life of an electrical storage device are extracted, the sensitivity of each factor is determined on the basis of a Taguchi method, which is a statistical method, and the life of the electrical storage device is predicted from the sensitivity (see, for example, Patent Literature 3).